As a heat exchanger such as a radiator, an evaporator or the like used for the refrigerating cycle, one provided with tubes for flowing a refrigerant and tanks with slots formed for insertion of the tube ends is known. The refrigerant is taken from a tank into the interior, performs heat exchange with heat conducted to the tubes and is discharged outside from the tank.
As the refrigerant for the refrigerating cycle, a fluorocarbon refrigerant including hydrochlorofluorocarbon has been used extensively. But it is now being replaced with CO2 considering the global environment in these years.
A refrigerating cycle using CO2 as the refrigerant has a very high inside pressure as compared with the refrigerating cycle using a fluorocarbon refrigerant, and particularly a pressure on a high-pressure side happens to exceed the critical point of the refrigerant depending on use conditions such as a temperature.
The critical point is a limit on the high-pressure side (namely, a limit on a high-temperature side) in a state that a gas layer and a liquid layer coexist and an end at one end of a vapor pressure curve. A pressure, a temperature and a density at the critical point become a critical pressure, a critical temperature and a critical density, respectively. Especially, when the pressure exceeds the critical point of the refrigerant in a radiator which is a high-temperature heat source of the refrigerating cycle, the refrigerant does not condense.
A heat exchanger used for such a supercritical refrigerating cycle is described in, for example, Japanese Patent Laid-Open Publication No. HEI 11-351783.
As to the heat exchanger for the refrigerating cycle, improvement of heat exchange efficiency of the refrigerant, miniaturization, weight reduction, facilitation of production and saving of mounting space are significant objects. Especially, a supercritical refrigerating cycle having a pressure on the high-pressure side exceeding the critical point of the refrigerant requires a very high compressive strength as compared with the refrigerating cycle using the fluorocarbon refrigerant. And the heat exchanger used therefor is required to secure pressure resistance and to be rationalized furthermore.
For example, the heat exchanger for the supercritical refrigerating cycle needs to reduce volumes of the tubes and the tanks and to increase their wall thickness in order to secure the pressure resistance. Therefore, it becomes somewhat difficult to fabricate the members constituting them, and it is desired that the individual component members are fabricated more efficiently at a heat exchanger manufacturing site.
The present invention has been made in view of the above circumstances and provides a heat exchanger which is configured rationally in conformity with the above-described subject so to be used for the supercritical refrigerating cycle.